Esterases tissue-specific distribution

In a number of papers the organ and tissue specificity distribution was described, for esterases (Markert and Hunter, 1959 Paul and Fottrell, 1961), acid phosphatase (Lundin and Allison, 1966), mitochondrial (M) and soluble (S) forms... 

Lund-Pero, M., Jeppson, B., Arneklo-Nobin, B., Sjogren, H.O., Holmgren, K. and Pero, R.W. (1994) Non-specific steroidal esterase activity and distribution in human and other mammalian tissues. ClinicaChimicaActa ... 

Loewi and Navratil have shown that ACh can be enzymatically inactivated by heart extracts (69). This, however, is not surprising, since, as pointed out by Stedman, Stedman, and Easson (127), esterases are widely distributed in the animal organism and are known to hydrolyze a variety of esters. The important question was whether there is an enzyme which specifically hydrolyzes ACh. Stedman, Stedman, and Easson (l.c.) prepared from horse serum an enzyme which they considered to be an esterase specific for ACh and called it choline esterase. Later investigations do not support the assumption that the enzyme prepared by Stedman, et al. is really a specific choline esterase. There exists, however, an esterase which is specific for ACh. The specificity may be demonstrated by testing the action of an esterase on a number of substrates. In this way, a pattern may be obtained which makes it possible to distinguish the specific choline esterase from other esterases. The esterase in all nerve tissue is either exclusively or predominantly choline esterase. The enzyme is extremely stable. If kept at low temperature and at neutral pH, its activity remains unchanged for many months. The specificity of the enzyme as w eil as other properties will be discussed elsewhere (Nachmansohn and Rothenberg, 131 Nachmansohn, 102). 

It was reported that the distribution and activities of esterases that catalyze pyrethroid metabolism using several human and rat tissues, including small intestine, liver, and serum, were examined [30]. The major esterase in human intestine was hCE2. //c/n.v-Permethrin was effectively hydrolyzed by pooled human intestinal microsomes (five individuals), while deltamethrin and bioresmethrin were not. This result correlated well with the substrate specificity of recombinant hCE2. In contrast, pooled rat intestinal microsomes (five animals) hydrolyzed trans-permethrin 4.5 times slower than the human intestinal microsomes. Furthermore, pooled samples of cytosol from human or rat liver were ca. half as hydrolytically active as the corresponding microsome fraction toward pyrethroids however, the cytosolic fractions had significant amounts (ca. 40%) of the total hydrolytic activity. Moreover, a sixfold interindividual variation in hCEl protein expression in human hepatic cytosols was observed. 

Many receptors have been identified in all cases they are proteins. Some of the proteins have enzymatic activity. Eor instance, dihydrofolate reductase is a receptor for antifolates and acetylcholine esterase is a receptor for organophosphates. Some receptors serve as transport vehicles across the cellular membranes, as is the case with the receptors for steroid hormones (Baxter and Eorsham, 1972). Specific receptors may be confined to certain tissues or may be distributed among all the cells of an organism. 

Human serum paraoxonase (PON 1) is an esterase that is physically associated with high-density lipoprotein (HDL) and is also distributed in tissues such as liver, kidney, and intestine [38,39]. Activities of PON 1, which are routinely measured, include hydrolysis of organophosphates, such as paraoxon (the active metabolite of the insecticide parathion) hydrolysis of arylesters, such as phenyl acetate and lactonase activities. Human serum paraoxonase activity has been shown to be inversely related to the risk of cardiovascular disease [40,41], as shown in atherosclerotic, hypercholester-olemic, and diabetic patients [42-44]. In 1998 HDL-associated PON 1 was shown to protect LDL, as well as the HDL particle itself, against oxidation induced by either copper ions or free radical generators [45,46], and this effect could be related to the hydrolysis of the specific lipoproteins oxidized lipids such as cholesteryl linoleate hydroperoxides and oxidized phospholipids. Protection of HDL from oxidation by PON 1 was shown to preserve... 

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